Phase gradient nanocomposite window fabrication and method of fabricating durable optical windows

ABSTRACT

An optical window is provided and includes a core layer, a cladding layer and an electromagnetic interference (EMI) layer interposed between the core and cladding layers.

DOMESTIC BENEFIT/NATIONAL STAGE INFORMATION

The present application is a non-provisional application that claims thebenefit of priority to U.S. provisional patent application Ser. No.62/404,526, which was entitled “PHASE GRADIENT NANOCOMPOSITE WINDOWFABRICATION AND METHOD OF FABRICATING DURABLE OPTICAL WINDOWS”, filed onOct. 5, 2016. The entire contents of U.S. provisional patent applicationSer. No. 62/404,526 are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a phase gradient nanocomposite windowfabrication method and a method of fabricating durable optical windows.

Optical windows used in aircraft and high-speed missiles must meet veryaggressive requirements on flexure strength, impact durability andoptical transparency. Often these constraints are in conflict such thatenvironmentally rugged windows lack sufficient transparency or spectralbandwidth for future generation optical search and track applications.

Optical windows can be produced by various processes that include, butare not limited to single crystal growth, chemical vapor deposition(CVD) and nanocomposite sintering. Nanocomposites, in particular, arevery attractive materials for use in windows because they can combinemultiple materials (or phases) to produce a window that is stronger thanthe windows produced from either phase alone. Nanocomposite-basedwindows are generally formed using a powder process which allows verylarge and curved window shapes to be produced in nearly finished shape.This is called near net shaping and in theory could be used to formwindows of any desired shape with minimal waste of materials. Otherwindow materials that employ single crystal growth or CVD require thatwindow fabrication start from a large block of material that is sculptedto produce the desired window topology. This is extremely expensive andtime consuming as well as being wasteful in terms of material usage.

When compared to the single phase (e.g., CVD) materials, thenanocomposites have certain disadvantages that weigh against their usedespite the benefits of near net shaping. For example, opticaltransparency of nanocomposite windows may suffer from increased opticalabsorption and scattering that is introduced by the added material orphase. That is, near net shape sintering of zinc sulfide (ZnS), forexample, produces a window that is mechanically weak and not normallyusable in airborne applications but, while the second phase of materialthat is added prevents large grain growth during sintering (a key tomaintaining hardness), the added hardening agent introduces scatteringand absorption effects. This occurs, in particular, in windows formed ofzinc sulfide and in windows including an additional second sulfidephase. Here, while mechanical strength of the window may be dramaticallyenhanced relative to pure sintered ZnS, the presence of the secondsulfide phase can cause strong optical absorption of radiation in a longwave infrared (LWIR) spectral band.

In addition, while certain coatings and electromechanical interference(EMI) treatment layers can be applied to certain windows, such coatingstend to be insufficiently durable. Meanwhile, although mechanicalshutters can be used to protect windows in some cases, shutters are notfeasible in all cases.

SUMMARY

According to an aspect of the invention, an optical window is providedand includes a core layer, a cladding layer and an electromagneticinterference (EMI) layer interposed between the core and claddinglayers.

In accordance with additional or alternative embodiments, the corelayer, the cladding layer and the EMI treatment layer have a curvedshape.

In accordance with additional or alternative embodiments, the core layerincludes a single phase material and the cladding layer includes ananocomposite optical ceramic.

In accordance with additional or alternative embodiments, the claddinglayer is at least 5 times harder than the core layer.

In accordance with additional or alternative embodiments, the EMItreatment layer includes at least one of an electrically conductive gridand an electrically conductive film.

According to another aspect of the invention, an optical window isprovided and includes multiple anti-reflection coatings, an outermostwindow layer interleaved between outermost and outer-intermediate onesof the multiple anti-reflection coatings, an innermost window layerinterleaved between innermost and inner-intermediate ones of themultiple anti-reflection coatings and an electromagnetic interference(EMI) treatment layer interleaved between the outer-intermediate andinner-intermediate anti-reflection coatings.

In accordance with additional or alternative embodiments, the multipleanti-reflection coatings, the outermost and innermost window layers andthe EMI treatment layer have a curved shape.

In accordance with additional or alternative embodiments, the outermostwindow layer includes nanocomposite optical ceramic material and theinnermost window layer includes a single phase material.

In accordance with additional or alternative embodiments, thenanocomposite optical ceramic has a distribution gradient ofnanocomposite formulations.

In accordance with additional or alternative embodiments, a material ofthe outermost window layer is harder than a material of the innermostwindow layer.

In accordance with additional or alternative embodiments, the EMItreatment layer includes at least one of a conductive grid and aconductive film.

In accordance with additional or alternative embodiments, one or more ofthe multiple anti-reflection coatings respectively include at least oneof a deposited geometric optic coating and a micro-textured physicaloptic coating.

In accordance with additional or alternative embodiments, an adhesivelayer is adjacent to the EMI treatment layer and includes at least oneor more of polyethylene, polystyrene, polypropylene, low meltingtemperature optical glass, paraffin, a thiol and a urethane.

In accordance with additional or alternative embodiments, an additionalanti-reflective coating is interposed between the innermost andinner-intermediate ones of the multiple anti-reflection coatings and isdisplaced from the inner-intermediate one of the multipleanti-reflection coatings to define a thermal mangement space.

According to yet another aspect of the invention, a method of assemblingan optical window is provided. The method including pre-processing corelayer material, disposing electromagnetic interference (EMI) treatmentlayer material onto the core layer material, providing cladding layermaterial to sandwich the EMI treatment layer material between thecladding layer material and the core layer material and post-processingat least the core layer material and the cladding layer material.

In accordance with additional or alternative embodiments, the core layermaterial, the EMI treatment layer material and the cladding layermaterial have a curved shape.

In accordance with additional or alternative embodiments, the claddinglayer material includes a nanocomposite optical ceramic (NCOC) and thecore layer material comprises a single phase material.

In accordance with additional or alternative embodiments, thepre-processing of the core layer material includes at least one or moreof sintering and hot isostatic pressurizing (HIPing).

In accordance with additional or alternative embodiments, the providingof the cladding layer material includes placing pre-processed core layermaterial and EMI treatment layer material in a fixture formed to set acladding layer thickness and depositing the cladding layer material intothe fixture.

In accordance with additional or alternative embodiments, the providingof the cladding layer material includes pre-processing the claddinglayer material.

In accordance with additional or alternative embodiments, thepost-processing of at least the core layer material and the claddinglayer material includes at least one or more of sintering and hotisostatic pressurizing (HIPing).

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts:

FIG. 1 is a side view of a unitary radome layer in accordance withembodiments;

FIG. 2 is a side view of a unitary radome layer in accordance withfurther embodiments;

FIG. 3 is a perspective view of a unitary radome layer in accordancewith alternative embodiments;

FIG. 4 is a perspective view of a unitary radome layer in accordancewith alternative embodiments;

FIG. 5 is a flow diagram illustrating a unitary radome layer assemblymethod in accordance with embodiments;

FIG. 6 is a schematic illustration of a centrifuge used to generate adistribution gradient in a unitary radome layer prior to curing orsintering in accordance with embodiments;

FIG. 7 is a schematic illustration of a centrifuge used to generate adistribution gradient in a unitary radome layer prior to curing orsintering in accordance with further embodiments;

FIG. 8 shows a side view of an optical window in accordance withembodiments;

FIG. 9 shows a side view of a simplified version of the optical windowin accordance with further embodiments;

FIG. 10 shows an EMI treatment layer of the optical windows of FIGS. 8and 9 in accordance with alternative embodiments;

FIG. 11 shows an EMI treatment layer of the optical windows of FIGS. 8and 9 in accordance with alternative embodiments;

FIG. 12 shows a side view of an optical window with a thermal managementspace in accordance with embodiments;

FIG. 13 is a flow diagram illustrating a method of assembling an opticalwindow in accordance with embodiments;

FIG. 14 is a schematic illustration of a fixture for providing anoptical window with a cladding layer in accordance with embodiments; and

FIG. 15 is a schematic illustration of a method of sandwiching an EMItreatment layer between core and cladding layers of an optical window inaccordance with embodiments.

DETAILED DESCRIPTION

As will be discussed below, potentially quite large and curved opticalwidows with excellent long-wave and mid-wave broadband transparency andhigh mechanical durability are provided. The windows are made of verydurable nanocomposite materials with high optical transparency and areformed based upon the fact that optical transparency is required of theentire bulk of the window while durability is only required at thesurface of the material that is exposed to environmental effects. Acentrifuge is used to increase the density of the hardening agent nearthe outer surface of the windows to increase mechanical strength whereit is most needed while reducing or eliminating the hardening agent inother areas of the window bulk. By maintaining less total volume ofhardener, the optical transparency of the window as a whole isrelatively improved. Meanwhile, by increasing the density of thehardener at the surface of the window, mechanical durability isimproved. The resulting optical and mechanical performance of the “phasegradient” nanocomposite window will exceed that of the currenttechnology and even allow new hardening agents to be introduced withoutstrongly or adversely affecting optical transparency. The use ofcentrifugal force generated by the centrifuge allows less opticallyabsorbing material to be used in the nanocomposite formulation whileactually increasing the mechanical strength of the window and itsdurability against rain, sand and other impacts. Ultrasonic agitationmay be added as a method for performing dry powder centrifugalsedimentation.

With reference to FIG. 1, a unitary radome layer assembly 10 is providedand includes a first nanocomposite formulation 11 and a secondnanocomposite formulation 12. The second nano-composite formulation 12has a hardener and a higher effective density than the firstnanocomposite formulation 11. The first nano-composite formulation 11may be but need not be more optically transparent than the secondcomposite nano-formulation 12 due at least in part to the lack of thehardener in the first nano-composite formulation. The first and secondnanocomposite formulations 11 and 12 are provided together in a unitaryradome layer 13 with each having a respective distribution gradientdefined relative to an axis or to multiple axes of the unitary radomelayer 13.

In accordance with embodiments and, as shown in FIG. 1, the unitaryradome layer 13 may be provided with a nose cone or ogive shape 14 thathas a pointed nose cone or ogive tip 140 and curved sidewalls 141extending in the aft direction from the pointed nose cone or ogive tip140. In these and other cases, the respective distribution gradients ofthe first and second nano-composite formulations 11 and 12 are definedrelative to a lateral axis A1 of the unitary radome layer 13 which isoriented transversely or perpendicularly with respect to a centrallongitudinal axis A2 of the unitary radome layer 13. That is, thelateral axis A1 may effectively define a first, front or forward portion15 of the unitary radome layer 13 as being any part of the unitaryradome layer 13 that is proximate to the nose cone or ogive tip 140 anda second, rear or aft portion 16 of the unitary radome layer 13 as beingany part of the unitary radome layer 13 that is remote from the nosecone or ogive tip 140.

To the extent that the second nanocompo site formulation 12 has thehardener and a higher effective density than the first nano-compositeformulation 11, the unitary radome layer 13 can be formed and cured(e.g., sintered) such that the distribution gradient of the secondnano-composite formulation 12 is characterized in that most of thesecond nano-composite formulation 12 is located in the forward portion15 and such that the distribution gradient of the first nano-compositeformulation 11 is characterized such that most of the firstnano-composite formulation 11 is located in the aft portion 16. Thesecharacterizations of the respective gradients have the followingresults.

With the first and second nano-composite formulations 11 and 12generally being located in the aft and forward portions 16 and 15,respectively, homogeneity within the forward and aft portions 15 and 16is increased and a tendency of the unitary radome layer 13 to scatter orabsorb electro-magnetic (EM) radiation is correspondingly reduced ascompared to what would otherwise occur if the first and secondnano-composite formulations 11 and 12 were distributed evenly throughoutthe unitary radome layer 13.

In addition, with the second nano-composite formulation 12 with thehardener being relatively harder than the first nano-compositeformulation 11 and being generally or mostly located in the forwardportion 15 where the unitary radome layer 13 is most likely toexperience impacts with foreign objects and where optical transmissionof signals through the unitary radome layer 13 is generally lessimportant, an overall strength and durability of the unitary radomelayer 13 is enhanced without sacrificing useful optical transparency.Meanwhile, with the first nano-composite formulation 11 being relativelymore optically transparent than the second nano-composite formulation 12and being generally or mostly located in the aft portion 16 whereoptical transmission of signals through the unitary radome layer 13 ismost important and where impacts are generally less common, an overalloptical transparency of the unitary radome layer 13 is enhanced withoutsacrificing strength or durability.

With reference to FIG. 2 and in accordance with further embodiments, theunitary radome layer 13 may be provided with the nose cone or ogiveshape 14 as in FIG. 1 but with the respective distribution gradients ofthe first and second nano-composite formulations 11 and 12 definedrelative to multiple axes of the unitary radome layer 13. In these orother cases, the multiple axes may include for example the lateral axisA1 and the central longitudinal axis A2. That is, while the lateral axisA1 may effectively define the forward and aft portions 15 and 16 of theunitary radome layer 13, the central longitudinal axis A2 may defineouter portions 17 of the unitary radome layer 13 as being those parts ofthe unitary radome layer 13 that are proximate to outer surfaces of thenose cone or ogive tip 140 and the sidewalls 141 and inner portions 18of the unitary radome layer 13 as being those parts of the unitaryradome layer 13 that are proximate to interior surfaces of the nose coneor ogive tip 140 and the sidewalls 141.

In the embodiments of FIG. 2, the unitary radome layer 13 can be formedand cured (e.g., sintered) such that the distribution gradient of thesecond nano-composite formulation 12 is characterized in that most ofthe second nano-composite formulation 12 is located along the outerportions 17 in the forward portion 15 and such that the distributiongradient of the first nano-composite formulation 11 is characterizedsuch that most of the first nano-composite formulation 11 is locatedalong the inner portions 18 in the aft portion 16.

In accordance with still further embodiments, the first nanocompositeformulation 11 may include yttrium oxide (Y₂O₃) particles of relativelysmall or first sizes (e.g., as measured in terms of mean or averageindividual particle diameters) S1 and the second nanocompositeformulation 12 may include magnesium oxide (MgO) particles of relativelylarge or second sizes (e.g., as measured again in terms of mean oraverage individual particle diameters) S2 where the second sizes S2 aregenerally larger than the first sizes S1. Thus, in the case of theembodiments of FIG. 1, the respective distribution gradients arecharacterized with an increased distribution of the Y₂O₃ particles ofthe first sizes S1 remote from the nose cone or ogive tip 140 in the aftportion 16 and an increased distribution of the MgO particles of thesecond sizes S2 proximate to the nose cone or ogive tip 140 in theforward portion 15. In the case of the embodiments of FIG. 2, therespective distribution gradients are characterized with an increaseddistribution of the Y₂O₃ particles of the first sizes S1 remote from thenose cone or ogive tip 140 and along the inner portions 18 in the aftportion 16 and an increased distribution of the MgO particles of thesecond sizes S2 proximate to the nose cone or ogive tip 140 and alongthe outer portions 17 in the forward portion 15.

With reference to FIGS. 3 and 4 and in accordance with embodiments, theunitary radome layer 13 may have at least one of a rounded (e.g.,spherical, hemispherical, etc.) shape 301 (see FIG. 3) and a flattenedshape 401 (see FIG. 4). In either or other cases, the unitary radomelayer 13 may include the first and second nano-composite formulations 11and 12, as noted above, with the respective distribution gradients.Thus, in exemplary cases, the unitary radome layer 13 with the roundedshape 301 of FIG. 3 may have an increased distribution of the firstnano-composite formulation 11 toward the interior surface of thecurvature and an increased distribution of the second nano-compositeformulation 12 toward the exterior surface of the curvature. Similarly,the unitary radome layer 13 with the flattened shape 401 of FIG. 4 mayhave an increased distribution of the first nano-composite formulation11 toward one side thereof and an increased distribution of the secondnano-composite formulation 12 toward the other side thereof.

With reference to FIG. 5, a unitary radome layer assembly method isprovided. The method initially includes designing a unitary radome layerwith first and second portions (such as the unitary radome layer 13 withthe nose cone or ogive shape 14 and the first, front or forward portions15 and the second, rear or aft portions 16 of FIGS. 1 and 2, the unitaryradome layer 13 with the rounded shape 301 of FIG. 3 or the unitaryradome layer 13 with the flattened shape 401 of FIG. 4) such that thefirst portions are more durable than the second portions and such thatthe second portions are more optically transparent than the firstportions (block 501). The method further includes providing first andsecond nanocomposite formulations together in a unitary radome layermold (such as a mold with a nose cone or ogive shape as in FIGS. 1 and2) where the second nanocomposite formulation has a hardener and ahigher effective density than the first nanocomposite formulation (block502). The method then includes an operation of generating respectivedistribution gradients for the first and second nanocompositeformulations prior to curing (e.g., sintering) (block 503).

In accordance with further embodiments and as shown in FIG. 5, themethod may also include controlling undesirable separation parameters ofthe first and second nanocomposite formulations (block 504) and anaddition of materials to at least one of the first and secondnanocomposite formulations to adjust at least one of respectiveeffective densities and respective sedimentation rates thereof (block505). The controlling of the undesirable separation parameters of block504 may include, for example, an ultrasonic assist process executed withrespect to the first and/or the second nano-composite formulations.

The first and second formulations may be suspended in fluid or providedas dry powders. In the latter case, it is to be understood that the drypowders may not be easily separated using centrifugal force. Here, anultrasonic agitator can be attached to the centrifuge to ultrasonicallyassist separation and dispersion processes. The ultrasonic agitationdisrupts attractive van der Walls forces between the particles of thefirst and second formulations to allow them to more easily migrate orglide through the volume. Also, since the hardener of the secondnano-composite formulation can tend to lower the effective density ofthe second nano-composite formulation, a third phase or material thatmay be optically benign can be added to the second nano-compositeformulation to increase the effective density of the secondnano-composite formulation beyond that of the first nano-compositeformulation.

In accordance with embodiments, the generating of the respectivedistribution gradients of block 503 may include defining the respectivedistribution gradients relative to a unitary radome layer axis, such asthe lateral axis A1 of FIGS. 1 and 2, or to multiple unitary radomelayer axes, such as the lateral axis A1 and the central longitudinalaxis A2 of FIGS. 1 and 2 (block 5031). In addition, the generating ofthe respective distribution gradients of block 503 may further includeplacing the unitary radome layer mold with the first and secondnanocomposite formulations in a centrifuge (block 5032) and activatingthe centrifuge to rotate the unitary radome layer mold with the firstand second nanocomposite formulations about the unitary radome layeraxis or about the multiple unitary radome layer axes (block 5033).

With reference to FIG. 6, the generating of the respective distributiongradients of block 503 is illustrated for the case of the unitary radomelayer 13 having the nose cone or ogive shape 14 and the respectivedistribution gradients being defined relative to the lateral axis A1. Inthis case, the unitary radome layer 13 is coupled to a centrifuge 601prior to curing of the curable material and the centrifuge 601 isactivated to rotate the unitary radome layer 13 about the lateral axisA1. Such rotation produces centrifugal forces that are applied to thefirst and second nano-composite formulations 11 and 12 that result inthe generation of an artificial gravitational field. Within thisartificial gravitational field, the first and second nano-compositeformulations 11 and 12 segregate from one another due to the secondnano-composite formulation 12 having the higher effective density suchthat the second nano-composite formulation 12 pools at the forwardportion 15 and the first nano-composite formulation 11 pools at the aftportion 16.

With reference to FIG. 7, in an event the centrifuge 601 of FIG. 6 weremodified to rotate the unitary radome layer 13 about the centrallongitudinal axis A2 or in an event the unitary radome layer 13 wereplaced into a new centrifuge, rotation of the unitary radome layer 13about the central longitudinal axis A2 prior to curing can lead to afurther pooling of the second nano-composite formulation 12 along theouter portions 17 in the forward portion 15 and a further pooling of thefirst nano-composite formulation 11 along the inner portions 18 in theaft portion 16.

It is to be understood that the invention described herein can beemployed jointly with EMI protection as explained below with referenceto FIGS. 8-15.

As will be discussed below, a durable optical window is provided for usein LWIR applications for example. A standard optical window with a corelayer formed of zinc sulfide (ZnS) is augmented with a nanocompositeoptical ceramic (NCOC) cladding layer. Both the core and the claddingmay be formed using NCOC powder-process sintering/HIPing processes. Thecladding is generally only thick enough to meet strength/impact goalswhile the bulk of the window is formed of the highly transparent ZnS. Inaddition, an electromagnetic interference (EMI) treatment layer isinterposed between the two core and cladding layers to provide EMIprotection. The EMI treatment layer may be a deposited films or amicrotextured (moth eye) grid on one or more surfaces. The durableoptical window may also include anti-reflection and adhesive layers.

With reference to FIG. 8, an optical window 10 is provided and includesmultiple anti-reflection coatings between which additional layers areinterleaved. In detail, the optical window 10 includes an outermostanti-reflection coating 11, an outer-intermediate anti-reflectioncoating 12, a cladding or outermost window layer (hereinafter referredto as an “outermost window layer”) 13 that is interleaved between theoutermost anti-reflection coating 11 and the outer-intermediateanti-reflection coating 12, an innermost anti-reflection coating 14, aninner-intermediate anti-reflection coating 15, a core or innermostwindow layer (hereinafter referred to as an “innermost window layer”) 16that is interleaved between the innermost anti-reflection coating 14 andthe inner-intermediate anti-reflection coating 15 and an EMI treatmentlayer 17.

The EMI treatment layer 17 is located or interleaved between theouter-intermediate anti-reflection coating 12 and the inner-intermediateanti-reflection coating 15. The EMI treatment layer 17 serves to providefor EMI protection for the optical window 10. In its positioninterleaved between the innermost anti-reflection coating 14 and theinner-intermediate anti-reflection coating 15, the EMI treatment layer17 is protected from external and/or environmental conditions for whichexterior EMI layers are not normally suitable.

The optical window 10 may further include an adhesive layer 18. Such anadhesive layer 18 may be disposed adjacent to the EMI treatment layer 17and may include at least one or more of polyethylene, polystyrene,polypropylene, low melting temperature glasses, a thiol and a urethane.

As shown in FIG. 8, the optical window 10 and the various components andlayers thereof may have a curved shape 101. More particularly, theoptical window 10 and the various components and layers thereof may havea nose-cone shape for provision at a forward end of an aircraft or amissile.

In accordance with embodiments, the outermost window layer 13 mayinclude nanocomposite optical ceramic (NCOC) material and, in somecases, may include multiple NCOC materials and possibly hardeningmaterials with one or more gradients defined therein. Meanwhile, theinnermost window layer 16 may include a single phase material, such asquartz or zinc sulfide (ZnS). In any case, the outermost window layer 13may be harder or substantially harder than the innermost window layer 16(e.g., the outermost window layer 13 may be up to 5 or more times harderthan the innermost window layer 16). The innermost window layer 16 maybe thicker or substantially thicker than the outermost window layer 13.

With reference to FIG. 9, which includes some but not all the featuresof FIG. 8 for purposes of clarity, a thickness of the optical window 20may be variable at various locations where the optical window 10 and thevarious components and layers thereof have a curved or nose-cone shape.For example, in the case of the optical window 10 having the nose-coneshape, the optical window 10 may have a maximum thickness T1 along acentral longitudinal axis A thereof a lesser thickness T2 at terminalside edges thereof and a decreasing thickness with increasing radialdistance from the central longitudinal axis A. In addition, as shown inFIG. 9, the innermost window layer 16 may be thicker than the outermostwindow layer 13 along the central longitudinal axis A and at theterminal side edges. Moreover, while the outermost window layer 13 andthe innermost window layer 16 both may exhibit decreasing thicknesseswith increasing radial distance from the central longitudinal axis, thedegree of the decrease may be more pronounced in the innermost windowlayer 16.

With continued reference to FIG. 8 and with additional reference toFIGS. 10 and 11, certain features of the EMI treatment layer 17 will nowbe described. As shown in FIG. 8, the EMI treatment layer 17 isinterposed between the outermost surface 150 of the inner-intermediateanti-reflection coating 15 and either an innermost surface 120 of theouter-intermediate anti-reflection coating 12 or an innermost surface(not shown) of the adhesive layer 18. The EMI treatment layer 17 may besubstantially thinner than the outermost window layer 13 and, in somecases, the innermost window layer 16 as well. The EMI treatment layer 17may exhibit greater losses as compared to either the outermost windowlayer 13 or the innermost window layer 16 but, since a thickness of theEMI treatment layer 17 is relatively small, such losses can be limited.In any case, the EMI treatment layer 17 may include or be formed as atleast one of a conductive grid 170 (see FIG. 10) and a conductive film171 (see FIG. 11).

In the case of the EMI treatment layer 17 being provided as a conductivegrid 170 as in FIG. 10, the outermost surface 150 of theinner-intermediate anti-reflection coating 15 may be micro-textured(e.g., as at least one of a deposited geometric optic coating patternand a micro-textured physical optic coating pattern) to form grooves inwhich the material of the EMI treatment layer 17 can sit. For example,the conductive grid 170 can be formed with a moth-eye pattern 20 wherethe outermost surface 150 (see FIG. 8) includes an array of raisedhexagonal protrusions 201 that are separated from one another byinter-protrusion grooves 202. During processing of the optical window10, materials of the EMI treatment layer 17 are disposed or depositedwithin these inter-protrusion grooves 202 and subsequently cured thereinto form the EMI treatment layer 17.

With reference to FIG. 12 and in accordance with further embodiments, anadditional anti-reflective coating 501 may be interposed between theinnermost anti-reflection coating 14 and the inner-intermediateanti-reflection coating 15. This additional anti-reflection coating 501may also be displaced from the inner-intermediate anti-reflectioncoating 15 to define a thermal management space 502 therebetween. Inoperational conditions, this thermal management space 502 may besupplied with coolant, such as air flow or fluid, or a heating element,such as an electrically resistive element, to maintain an appropriateoperating temperature of the optical window 10.

With reference to FIG. 13, a method of assembling an optical window,such as the optical window 10 with the curved shape as described herein,is provided. As shown in FIG. 13, the method includes pre-processingcore layer material (block 601), disposing electromagnetic interference(EMI) treatment layer material onto the core layer material (block 602),providing cladding layer material to sandwich the EMI treatment layermaterial between the cladding layer material and the core layer material(block 603) and post-processing at least the core layer material and thecladding layer material (block 604). As noted above, the cladding layermaterial may include a nanocomposite optical ceramic (NCOC) and, in somecases, may include multiple NCOC materials and possibly hardeningmaterials with one or more gradients defined therein, and the core layermaterial may include a single phase material such as zinc sulfide (ZnS).

In accordance with embodiments, the pre-processing of the core layermaterial and the cladding layer material of block 601 and 603 mayinclude at least one or more of sintering and hot isostatic pressurizing(HIPing). Similarly, the post-processing of at least the core layermaterial and the cladding layer material of block 604 may include atleast one or more of sintering and HIPing.

With reference to FIG. 14 and in accordance with embodiments, theproviding of the cladding layer material of block 603 may includeplacing pre-processed core layer material and EMI treatment layermaterial in a fixture 701 that is formed to set a cladding layerthickness and subsequently depositing the cladding layer material intothe space 702 in the fixture 701 between the pre-processed core layermaterial and the EMI treatment layer material.

With reference to FIG. 15 and in accordance with alternativeembodiments, the providing of the cladding layer material of block 603may include pre-processing both the core layer material and the claddinglayer material, sandwiching the EMI treatment layer material between thecore and cladding layer materials and at least one or more of sinteringand HIPing the various layers together.

It is to be understood that the invention described herein can beemployed jointly with a phase gradient nanocomposite layer.

While the preferred embodiments to the invention have been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. An optical window, comprising: a core layer; acladding layer; and an electromagnetic interference (EMI) layerinterposed between the core and cladding layers.
 2. The optical windowaccording to claim 1, wherein the core layer, the cladding layer and theEMI treatment layer have a curved shape.
 3. The optical window accordingto claim 1, wherein the core layer comprises a single phase material andthe cladding layer comprises a nanocomposite optical ceramic.
 4. Theoptical window according to claim 1, wherein the cladding layer is atleast 5 times harder than the core layer.
 5. The optical windowaccording to claim 1, wherein the EMI treatment layer comprises at leastone of an electrically conductive grid and an eleectrically conductivefilm.
 6. An optical window, comprising: multiple anti-reflectioncoatings; an outermost window layer interleaved between outermost andouter-intermediate ones of the multiple anti-reflection coatings; aninnermost window layer interleaved between innermost andinner-intermediate ones of the multiple anti-reflection coatings; and anelectromagnetic interference (EMI) treatment layer interleaved betweenthe outer-intermediate and inner-intermediate anti-reflection coatings.7. The optical window according to claim 6, wherein the multipleanti-reflection coatings, the outermost and innermost window layers andthe EMI treatment layer have a curved shape.
 8. The optical windowaccording to claim 6, wherein the outermost window layer comprisesnanocomposite optical ceramic material and the innermost window layercomprises a single phase material.
 9. The optical window according toclaim 8, wherein the nanocomposite optical ceramic has a distributiongradient of nanocomposite formulations.
 10. The optical window accordingto claim 6, wherein a material of the outermost window layer is harderthan a material of the innermost window layer.
 11. The optical windowaccording to claim 6, wherein the EMI treatment layer comprises at leastone of an electrically conductive grid and an electrically conductivefilm.
 12. The optical window according to claim 6, wherein one or moreof the multiple anti-reflection coatings respectively comprise at leastone of a deposited geometric optic coating and a micro-textured physicaloptic coating.
 13. The optical window according to claim 6, furthercomprising an adhesive layer adjacent to the EMI treatment layer, theadhesive comprising at least one or more of polyethylene, polystyrene,polypropylene, low melting temperature optical glass, paraffin, a thioland a urethane.
 14. The optical window according to claim 6, wherein: anadditional anti-reflective coating is interposed between the innermostand inner-intermediate ones of the multiple anti-reflection coatings,and the additional anti-reflective coating is displaced from theinner-intermediate one of the multiple anti-reflection coatings todefine a thermal management space.
 15. A method of assembling an opticalwindow, the method comprising: pre-processing core layer material;disposing electromagnetic interference (EMI) treatment layer materialonto the core layer material; providing cladding layer material tosandwich the EMI treatment layer material between the cladding layermaterial and the core layer material; and post-processing at least thecore layer material and the cladding layer material.
 16. The methodaccording to claim 15, wherein the core layer material, the EMItreatment layer material and the cladding layer material have a curvedshape.
 17. The method according to claim 15, wherein the cladding layermaterial comprises a nanocomposite optical ceramic (NCOC) and the corelayer material comprises a single phase material.
 18. The methodaccording to claim 15, wherein the pre-processing of the core layermaterial comprises at least one or more of sintering and hot isostaticpressurizing (HIPing).
 19. The method according to claim 15, wherein theproviding of the cladding layer material comprises: placingpre-processed core layer material and EMI treatment layer material in afixture formed to set a cladding layer thickness; and depositing thecladding layer material into the fixture.
 20. The method according toclaim 15, wherein: the providing of the cladding layer materialcomprises pre-processing the cladding layer material, and thepost-processing of at least the core layer material and the claddinglayer material comprises at least one or more of sintering and hotisostatic pressurizing (HIPing).